Dissertations / Theses: 'Neutron emissions'

1

Khrbish, Yabia Saleh. "Application of neutron and proton induced prompt emissions for elemental analysis." Thesis, University of Surrey, 1987. http://epubs.surrey.ac.uk/844238/.

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The principles of neutron and proton induced reactions and their application to elemental analysis are described. Prompt Gamma-ray Neutron Activation Analysis (PGNAA) as a relatively rapid technique for the determination of trace amounts (ppm) of B and Cd is given. The need to establish the absolute method of analysis is investigated through the evaluation of the K-factor which acts as a monitor on the reliability of the various parameters involved in the absolute method. The neutron flux and detector efficiency are characterised and flux non-uniformity and detection efficiency for extended sources are discussed through the development of a Monte Carlo technique which enables us to calculate the geometric and effective solid angles subtended by a collimated detector at cylindrical and disc shaped sources or targets. Use of protons with energies ≤ 2 MeV to induce nuclear reactions which emit prompt alpha particles and gamma-rays is applied to the elemental analysis of various matrices. Although this technique is a surface and near surface analysis, it serves to confirm the results obtained by PGNAA as well as to indicate the non-uniformity of the elemental distribution along the sample surface scanned. This is demonstrated for a number of plant samples and a human tooth enamel. Detection of prompt alpha particles emitted necessitates the use of absorber foils to stop the high flux of backscattered protons from reaching the alpha detector. The broadening the introduction of such foils cause to the measured alpha spectra is also experimentally determined.

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2

Steer, Steven John. "Isomer decay spectroscopy of N<126 neutron-rich nuclei." Thesis, University of Surrey, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.493243.

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Thomson, Brent Wayne. "Determining the origin and possible mechanisms of QPOS in x-ray emissions of neutron stars and black holes." Thesis, The University of North Dakota, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=3681134.

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QPOs (Quasi-Periodic Oscillations) are time oscillations that appear in the light curve of observational data in x-ray bands. They are of mysterious origin although they are believed to be a result of the intense gravity around neutron stars and black holes and emit x-rays from accretion disks. I investigate a derived ratio between two periods has been found in the QPO data. The two periods, which appear as peaks in the power density spectrum have been found to be in a 3:2 ratio and can possibly distinguish theoretical models. In the work presented here, two physical approaches are developed that can explain the integer resonance ratio. One is a cusp layer model, which is based on a boundary layer model that uses the physical conditions at opposite sides of said layer to explore the magnitude of the vertical versus radial epicyclic frequencies and confirm the anticipated scales of the observed frequencies. It also happens to recreate a 3:2 resonance ratio for the Keplerian angular frequencies at the ISCO, taken as the preferred radius for the boundary layer model.

A toy model was recreated and utilized to emulate the Alfven radius due to the accretion disk's innate magnetic field and explore how it serves as a disruption radius and impacts the accretion of mass and the effective inner edge of the disk. The simulations show that there is no significance deviation from the ISCO as an effective inner edge for the accretion disk due to the magnetospheric influence of the disk alone.

I also invoke a parameter to handle the coupling between the vertical and radial epicyclical frequencies and relate it to the pressure within the disk. I show the coupling is strongest at the equatorial plane where pressure is at its maximum value.

A model I utilize is a relativistic resonance model, combined with a helioseismological approach to explore the pulsation of the inner edge of the accretion disk that imparts the resonance of the accreting matter moving along the Kerr space-time orbits. The helioseismological model gives a characteristic frequency for small perturbations in the stellar matter within the atmosphere of a star. The diskoseismological model extends that principle to material within an accretion disk. I take it to the same extent that the QPO frequencies are due to small perturbations along the marginally stable circular orbit, in the vertical and radial directions and use it as a probe into the inner disk and what information it yields. The inner disk edge, per the model, is treated as a vibrating surface that yields the radial and vertical epicyclic frequencies as characteristic features of the vibration. The epicyclical frequencies found using the physical parameters of the model within the cusp layer inside the disk could explain the physical context of the phenomenon responsible for the creation of the QPOs. An approach within the diskoseismological model uses the cylindrical reference frame of a disk in terms of the distribution of mass in combination with the strong gravity of the central object and the Keplerian velocity and sonic speed to yield a natural resonance ratio of 3/2 as well.

The model can be used as a diagnostic tool to explore the physical phenomena of the material orbits and the disk itself. Most importantly, the model can be used to determine and constrain the ratio of spin to mass of the compact object itself. It yields new information as previously undetermined by any earlier model; the adiabatic index at a specific radius within the accretion disk, which serves to lend insight into the innate phenomena of accretion disks at large. It establishes what were previously unknown information, such as the mass density distribution at a specific radius and outward, the radius of influence in terms of the sonic radius, the accretion rate, and the temperature distribution at the same radius for the accretion disk, as all are dependent on the adiabatic index. In all previous literature, the adiabatic index is taken as an assumptive estimate, and the models build on that assumed value of the adiabatic index. This model allows us to obtain an actual value of the adiabatic index at the ISCO and use it as an establishing feature to refine models on for more physically realistic observations.

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Ryan, James. "Measuring the energies and multiplicities of prompt gamma-ray emissions from neutron-induced fission of 235 U using the STEFF spectrometer." Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/measuring-the-energies-and-multiplicities-of-prompt-gammaray-emissions-from-neutroninduced-fission-of-235-u-using-the-steff-spectrometer(5fca332e-58ef-463f-96ba-99d87f0ecf44).html.

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Following a NEA high priority nuclear data request, an experimental campaign to measure the prompt Î3-ray emissions from 235 U has been performed. This has used the STEFF spectrometer at the new Experimental Area 2 (EAR2) within the neutron time- of-flight facility (n_TOF), a white neutron source facility at CERN with energies from thermal to approximately 1 GeV. Prior to the experimental campaign, STEFF has been optimised for the environment of EAR2. The experimental hall features a high background Î3-ray rate, due to the nature of the spallation neutron source. Thus an investigation into reduction of the background Î3-ray rate, encountered by the NaI(Tl) detector array of STEFF, has been carried out. This has been via simulations using the simulation package FLUKA. Various materials and shielding geometries have been investigated but the effects determined to be insufficient in reducing the background rate by a meaningful amount. The NaI(Tl) detectors have been modified to improve their performance in a high count rate environment, and their behaviour characterised to understand the response to higher count rates. Initial testing demonstrated that the modified detectors maintain a potential to measure Î3-ray multiplicities up to 3 counts per microsecond. However, the energy resolution fails somewhere below 1.75 counts per microsecond. The experimental campaign has produced a large amount of data. The preliminary analysis of phase one data has considered incoming neutron energies ranging from thermal to an upper limit of 1 eV, with a minimum Î3-ray energy threshold of 160 keV. Results have been achieved for the prompt fission Î3-ray multiplicity and total energy of M Î3 = 6.3 Â± 0.2 and E S,Î3 = 9.0 Â± 0.1 MeV respectively. Further work is ongoing by the STEFF team at Manchester to improve upon these results and analyse the remainder of the data set at higher incoming neutron energies.

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Snowden, Mareena Robinson. "Nuclear warhead monitoring : a study of photon emissions from fission neutron interactions with high explosives as a tool in arms control verification." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/113723.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2017.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references.
Since the signing of the Nuclear Nonproliferation Treaty, the technical community has been working to develop verification options that provide confidence in the reduction or elimination of nuclear warheads, while respecting countries' requirement of limited access to national secrets. This dissertation used a simplified open-source warhead model as a vehicle to investigate the use of secondary gammas, generated passively by neutron interactions inside high explosive (HE), as a signature for the presence of a warhead-like object. Analytical calculations were done to estimate the detectability of radiative capture and inelastic scatter emissions generated within the warhead model. Results showed the emission of gammas from nitrogen, between 5-7 MeV, to be detectable above background with dwell-times exceeding 90 minutes. These calculations motivated the systematic study of the signal experimentally using surrogate materials to represent the warhead's weapons-grade plutonium and HE. The experiment did not show the expected signals. This motivated a simulation of the mock-up experiment using the radiation transport code MCNP6 to help understand the observed results. The experimental and simulation data suggest that correlated backgrounds from neutron interactions with environmental materials dominate the signal. This finding helped provide a basis for understanding the feasibility and challenges to detecting this neutron-induced gamma signal. Three sets of pulse-height spectra have been analyzed: experimental spectra that looked at the effect of the HE surrogate on the overall detected counts; simulated spectra that helped to understand the underlying contributors to the observed experimental result; and a data-MCNP6 comparison that assessed the accuracy of the simulated results. Each set contributed to the quantification of detectability for the emissions of interest. The findings suggest the passive detection of the expected high-energy gamma signal is not feasible, unless backgrounds can be better controlled. The difficulty is attributed to low solid-angle coverage of the neutron source by the melamine explosive surrogate, and competing backgrounds produced by neutron-source interactions with surrounding materials. This thesis also examined the benefits and tradeoffs of this particular verification approach by investigating the non-technical context of the verification, such as the preferences of negotiators. The tradeoffs between confidence and intrusiveness highlight the need for technical verification solutions that span the diversity of options. Factors limiting the development of warhead verification systems, from the bias of researchers to issues of classification and sensitive geometries, were discussed.
by Mareena Robinson Snowden.
Ph. D.

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Kundu, Anu. "Contribution of multipolar electromagnetic fields to the radio and high energy emission of pulsars." Thesis, Strasbourg, 2018. http://www.theses.fr/2018STRAE014/document.

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L'étude du champ électromagnétique autour des étoiles à neutrons est l'une des méthodes vitales pour comprendre la physique des pulsars. Alors que la plupart des publications utilisent l'hypothèse d'un champ électromagnétique dipolaire centré standard, des études récentes se sont concentrées sur l'inclusion de composantes de champ multipolaire plus élevées et ont présenté une image plus générale pour les pulsars dans lesquels le moment du dipôle magnétique est décalé du centre de l'étoile. Ce travail discute des conséquences d'un dipôle magnétique rotatif excentré dans le vide en montrant diverses caractéristiques des lignes de champ magnétique et de l'émission de pulsar. Une étude à large bande du spectre du rayonnement pulsar est également présentée par la création de cartes des différentes régions d'émission des pulsars distinguées sur la base de leur fréquence dans le but principal de rechercher l'évolution du profil d'impulsion avec la fréquence. La thèse présente tous les résultats ci-dessus accompagnés des discussions nécessaires pour comprendre les modèles théoriques utilisés et les détails des méthodes numériques appliquées
Studying the electromagnetic field around neutron stars is one of the vital methods to understand the physics of the pulsars. While major literature uses assumption of a standard centred dipolar electromagnetic field, recent studies have focused on including higher multipolar field components and have presented a more generalized picture for pulsars in which the magnetic dipole moment is shifted off from the centre of the star. This work discusses the consequences of an off centred rotating magnetic dipole in vacuum by showing various characteristic features of magnetic field lines and pulsar emission. A broadband spectrum study of pulsar radiation is also laid out by creating maps of different emission regions of pulsars distinguished on the basis of their frequency with the main aim of looking for the evolution of the pulse profile with frequency. The thesis presents all the above results accompanied by the necessary discussions to understand the theoretical models used and the details of the numerical methods applied

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Klimek, Iwona. "Modelling and Measurements of MAST Neutron Emission." Doctoral thesis, Uppsala universitet, Tillämpad kärnfysik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-282122.

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Measurements of neutron emission from a fusion plasma can provide a wealth of information on the underlying temporal, spatial and energy distributions of reacting ions and how they are affected by a wide range of magneto-hydro-dynamic (MHD) instabilities. This thesis focuses on the interpretation of the experimental measurements recorded by neutron flux monitors with and without spectroscopic capabilities installed on the Mega Ampere Spherical Tokamak (MAST). In particular, the temporally and spatially resolved measurements of the neutron rate measured by the neutron camera, which also possesses spectroscopic capabilities, are combined with the temporally resolved measurements of the total neutron rate provided by the absolutely calibrated fission chamber in order to study the properties of the fast ion distributions in different plasma scenarios. The first part of the thesis describes in detail the two forward modelling methods, which employ the set of interconnected codes developed to interpret experimental observations such as neutron count rate profiles and recoil proton pulse height spectra provided by the neutron camera. In the second part of the thesis the developed methods are applied to model the neutron camera observations performed in a variety of plasma scenarios. The first method, which involves only TRANSP/NUBEAM and LINE2 codes, was used to validate the neutron count rate profiles measured by the neutron camera in three different plasma scenarios covering the wide range of total neutron rate typically observed on MAST. In addition, the first framework was applied to model the changes in the total and local neutron rates caused by fishbone instability as well as to estimate the Hydrogen and Deuterium ion ratio. The second modelling method, which involves TRANSP/NUBEAM, LINE2, DRESS and NRESP, was used to validate the measured recoil proton pulse height spectra in a MHD-quiescent plasma scenario.

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Taverna, Roberto. "Polarized emission from highly-magnetized neutron stars." Doctoral thesis, Università degli studi di Padova, 2016. http://hdl.handle.net/11577/3424483.

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The study of magnetars, the anomalous X-ray pulsars (AXPs) and the soft gamma repeaters (SGRs), and of X-ray Dim Isolated Neutron Stars (XDINSs) is of particular relevance, since these objects exhibit the strongest magnetic fields ever observed in the universe (10^13-10^15 G) and represent the only laboratories where physics in the presence of such strong magnetic fields can be tested. Until now, these peculiar neutron stars have been investigated through spectroscopic and timing measurements, which led to validate the theoretical models developed to explain their phenomenology, as in the case of the "twisted magnetosphere'' model for magnetars or the different surface emission models for XDINSs. Nevertheless, this kind of analysis alone is far from providing complete information. In this respect, X-ray polarimetry may disclose an entirely new approach in the study of highly magnetized neutron stars. Radiation emitted in the presence of strong magnetic fields, in fact, is expected to be highly polarized; polarization measurements provide two additional observables, the linear polarization fraction and the polarization angle, that can unambiguously determine the model parameters also when spectral analysis alone fails. The polarization signal that an observer at infinity would collect, however, do not necessary coincide with model predictions for the polarization at the surface, due to the effects of quantum electrodynamics in the highly magnetized vacuum around the star, coupled with the rotation of the Stokes parameters in the plane perpendicular to the line of sight, induced by the non-uniform magnetic field. In this thesis I present the results of the numerical codes I developed to simulate the polarization pattern, both at the surface and as observed at infinity, of the radiation emitted from highly magnetized, isolated neutron stars, using as templates the bright AXP 1RXS J170849.0-400910 and the XDINS RX J1856.5-3754. I demonstrate that polarization measurements can indeed provide key information about the physical and geometrical properties of these sources, allowing to directly test theoretical models. This work is also relevant in view of the launch of new-generation X-ray polarimeters, currently under development, like the X-ray Imaging Polarimeter Explorer (XIPE). For this reason, I also compare theoretical models with XIPE simulated observations, in order to show how polarization measurements can be used to extract the values of magnetospheric parameters and viewing angles.
Lo studio delle magnetars, anomalous X-ray pulsars (AXPs) e soft gamma repeaters (SGRs), e delle X-ray Dim Isolated Neutron Stars (XDINSs) è di particolare rilevanza, dal momento che questi oggetti mostrano i più forti campi magnetici mai osservati nell'universo (10^13-10^15 G) e rappresentano i soli laboratori dove la fisica in presenza di campi magnetici così forti può essere testata. Fino ad ora, queste particolari stelle di neutroni sono state studiate attraverso misure spettroscopiche e di timing, che hanno portato a corroborare i modelli teorici formulati per spiegare la loro fenomenologia, come nel caso del "twisted magnetosphere'' model per le magnetars o dei diversi modelli di emissione superficiale per le XDINSs. Cionondimeno, questa analisi da sola non riesce a fornire informazioni complete. A questo riguardo, la polarimetria X può svelare un approccio completamente nuovo nello studio delle stelle di neutroni altamente magnetizzate. La radiazione emessa in presenza di forti campi magnetici, infatti, è attesa essere altamente polarizzata; le misure di polarizzazione forniscono due osservabili aggiuntivi, la frazione di polarizzazione lineare e l'angolo di polarizzazione, che possono determinare senza ambiguità i parametri dei modelli anche quando la sola analisi spettrale si dimostra insufficiente. Il segnale di polarizzazione che un osservatore riceve all'infinito, tuttavia, non coincide necessariamente con ciò che i modelli predicono per la polarizzazione alla superficie, a causa degli effetti dell'elettrodinamica quantistica nel vuoto fortemente magnetizzato attorno alla stella, accoppiato con la rotazione dei parametri di Stokes nel piano perpendicolare alla linea di vista, indotta dal campo magnetico non uniforme. In questa tesi presento i risultati dei codici numerici che ho sviluppato per simulare il pattern di polarizzazione, sia alla superficie che all'infinito, della radiazione emessa da stelle di neutroni isolate altamente magnetizzate, usando come modelli la luminosa AXP 1RXS 170849.0-400910 e la XDINS RX J1856.5-3754. Dimostrerò che le misure di polarizzazione possono effettivamente fornire informazioni cruciali sulle proprietà fisiche e geometriche di queste sorgenti, permettendo di testare direttamente i modelli teorici. Questo lavoro è inoltre rilevante in vista del lancio di polarimetri X di nuova generazione, attualmente in fase di sviluppo, come l'X-ray Imaging Polarimetry Explorer (XIPE). Per questa ragione, confronterò i modelli teorici con osservazioni simulate di XIPE, allo scopo di mostrare come le misure di polarizzazione possono essere utilizzate per estrarre i valori dei parametri relativi alla magnetosfera e gli angoli di vista.

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Chietera, Andreina. "Angular correlations between fragments and neutrons in the spontaneous fissions of 252 Cf." Thesis, Strasbourg, 2015. http://www.theses.fr/2015STRAE048/document.

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L'objectif de cette thèse est d'explorer les mécanismes d'émission des neutrons émis lors du processus de la fission. En particulier, la question ouverte de l'existence d'une anisotropie dynamique dans le centre de masse des fragments de fission et/ou de la possibilité d'une émission de neutrons de scission est explorée. La thèse débute par une introduction aux concepts théoriques permettant de décrire les processus de fission et les mécanismes d'émission de neutrons. La nécessité de concevoir une méthode d'analyse appropriée pour caractériser des mécanismes très subtiles est discutée, en insistant sur l'importance de maîtriser les biais expérimentaux. Le travail effectué a exigé un effort important de simulation, à travers le développement d'une procédure Monte Carlo pour décrire la fission spontanée du 252Cf, ainsi qu'une modélisation du dispositif expérimental de l'expérience CORA3.Nous proposons pour la première fois une approche simultanée et indépendante des deux mécanismes, émission de scission et anisotropie dynamique, ainsi que des valeurs quantitatives d'anisotropie et d'émission de scission mesurées expérimentalement
The subject of this thesis is to explore the neutron emission mechanisms in the fission process. In particular a long standing open question, the existence of a dynamical anisotropy in the centre of mass of the fission fragments and/or a possible scission neutron emission is explored. The thesis starts with an overview of the theoretical concepts on the fission process and on the neutron emission mechanisms. Also the necessity to conceive an appropriate analysis method is stressed when a very subtle mechanism is studied as various approximations and/or experimental biases not completely handled can hide the physical phenomena. In the presented work a huge effort was required to write a Monte Carlo procedure based on a coherent model for the spontaneous fission of 252Cf and to couple it with the devices exploited in the CORA3 experiment

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GILIBERTI, ELIA. "ON NEUTRON STARS'CRUST BREAKING AND GRAVITATIONAL WAVES EMISSION." Doctoral thesis, Università degli Studi di Milano, 2020. http://hdl.handle.net/2434/704603.

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Many different astrophysical events related to pulsars are taught to be due to starquakes, that could be caused by various possible loadings acting on the crust. However, at the present time, there is still a lack of theoretical well based modelling for most of these loadings and, therefore, we have only a very rough knowledge of the physics of neutron stars’ crust response. This PhD work wants to be a first development of a quite realistic calculation of the effects of chosen loadings, being that the forces due to uniform rotation, differential rotation or pinning, on the crust of pulsars. A Newtonian model, already used in Geophysics, has been adapted to the very different physical conditions of neutron stars’ physics and used to describe self-gravitating neutron stars, both in the incompressible and compressible scenario, subjected to different kinds of loadings. In particular, the deformations due to uniform rotation, differential rotation and slack pinning are studied. It is found that the response of the star is very sensitive to the adiabatic index value, while it is weakly influenced by the stellar mass. In all the cases, the strain developed between two glitches is found to be insufficient to break the crust, a result that challenges the standard picture of pulsar glitches based on crustquakes. Finally, attention is focused on accreting neutron stars in low-mass X-ray binaries and millisecond pulsars. The scenario is the following: the star spins up due to the accretion of matter thus building up stress; the mass quadrupole moment associated with crustal failures leads to the emission of gravitational waves which, in turn, spins down the star until equilibrium. The equilibrium frequency calculated is found compatible with observations. It is also argued that these gravitational waves could be potentially detected by the LIGO-Virgo interferometers in the near future.

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Agerhäll, Isabella, Malin Kindmark, and Cecilia Stern. "Towards Climate Neutral Facility Management : Improved Greenhouse Gas Emission Calculations for Ihus." Thesis, Uppsala universitet, Institutionen för samhällsbyggnad och industriell teknik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-413768.

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Uppsala municipality has set a goal in line with the UN’s 2030 Agenda for sustainable development to be fossil-free by 2030. To achieve this a lot of local companies have signed the Uppsala Climate Protocol. One of these companies is the municipal facility management company AB Uppsala Kommun Industrihus, Ihus. This project aimed to help Ihus map their emissions connected to facility maintenance and management and to enable them to reach their goal of becoming climate neutral by 2030. The daily facility management was split up into the categories gardening, ventilation and installation, cleaning and facility work, materials and products, renovations, and painting. A sustainability spend analysis was performed on Ihus’ organisation and emissions per spent MSEK were calculated for each category by researching Ihus’ suppliers. By using those emission intensities, the two categories with the highest emissions could be identified as renovations and materials and products with intensities of 84.48 and 57.56 tonnes CO2e/MSEK, respectively. The remaining categories all had intensities below 3 tonnes CO2e/MSEK. Sensitivity analyses were performed on the results by tweaking the values of which the emissions were based on. The results showed that to lessen Ihus’ climate impact the areas of improvement are life cycle assessments for their facilities and overseeing transports.

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Balogun, Fatai Akintunde. "Compton scattering and neutron induced gamma-ray emission tomography." Thesis, University of Surrey, 1986. http://epubs.surrey.ac.uk/842882/.

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Since the first introduction of reconstructive tomography in medicine more than a decade ago, research into this technique has continued to arrest the interest of a growing number of scientists especially in the area of industrial non-destructive testing. It is thus an advantage for a laboratory to have a test rig that combines the various Imaging modalities using ionising radiations. Such a test rig has been designed and built around a BBC-B microcomputer complete with its own display system. It combines the ability for transmission and emission tomography with a capability for Compton scattering imaging. Imaging characteristics of the rig including the detectors efficiency, response, collimating systems line spread functions, resolution and the modulation transfer functions are determined. A model has been established to numerically calculate accurately the scattering volume and predict the scattering field at any scattering angle for bore-hole type of collimation. Images of aluminium phantom with lead and brass inclusions have been used to demonstrate the particular suitability of the Compton scattering technique for detecting dense materials within a low density medium. The use of an attenuation correction method for the scattered photons has proved very successful in improving contrast and signal-to-noise ratio of the images. None of the established imaging methods has proved capable of elemental distribution analysis and the methods used in elemental analysis lack the spatial information provided in imaging. A new and novel method is presented in this work that combines the elemental capability of neutron activation analysis with the spatial information of emission tomography. This method has been termed neutron induced gamma-ray emission tomography (NIGET). NIGET images obtained of a freeze-dried water pellet, a piece of human tibia and a study of the diffusion of a preservative solution in a sample of Scots-pine, have been used to demonstrate the potentials of this method.

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Field, G. M. "Pre-equilibrium processes in nuclear reactions." Thesis, University of Oxford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233509.

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Toner, Mark P. "High energy neutral emissions from solar flares." Thesis, University of Glasgow, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.412948.

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Chen, Yong. "Delayed neutron emission measurements for U-235 and Pu-239." Thesis, [College Station, Tex. : Texas A&M University, 2006. http://hdl.handle.net/1969.1/ETD-TAMU-1134.

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Hellesen, Carl. "Diagnosing Fuel Ions in Fusion Plasmas using Neutron Emission Spectroscopy." Doctoral thesis, Uppsala universitet, Tillämpad kärnfysik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-114449.

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Neutron emission spectra, measured with the time of ﬂight spectrometer TOFOR, at the joint European torus (JET) are presented in this thesis. TOFOR has been in use since 2005, routinely measuring the neutron emission from JET plasmas. The work in the thesis mainly concerns the modeling of the signatures in the neutron spectrum that reveal different parts of the fuel ion distribution, such as the thermal bulk plasma as well as energetic ions from neutral beam and ion cyclotron heating. Parametric models of the signatures, using plasma parameters as input, are employed to generate trial neutron spectra. The parameters, such as the fuel ion temperature or the fast ion distribution function, are deduced by iteratively ﬁtting the trial spectra to the measured data. Measurements with TOFOR have been made and the models were applied. The studies are mainly on neutrons from d(d, n)3 He reactions(DD), although the emission from reactions with the plasma impurity 9 Be and triton burn up is covered as well. This has allowed for detailed studies of e.g. the physics ICRF heating as well as the interactions between energetic ions and plasma instabilities, such as toroidal Alfvé Eigenmodes.

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Nadel-Turonski, Pawel. "Experimental Studies of Neutron Emission Induced by Heavy-Ion Scattering." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-3570.

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Higgins, Mark. "Gamma-ray emission from neutron stars and the Deutsch field pulsar." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq20564.pdf.

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Daniels, Graham Clinton. "Observing flow using fast neutron radiography and positron emission particle tracking." Doctoral thesis, Faculty of Science, 2021. http://hdl.handle.net/11427/33606.

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Dynamic flow of material has been studied using fast neutron radiography (FNR) and positron emission particle tracking (PEPT). A new fast neutron imaging system was commissioned at The South African Nuclear Energy Corporation, Pretoria, as part of this study, although FNR measurements were ultimately performed at PhysikalischTechnische Bundesanstalt (PTB), Braunschweig. The PEPT studies were undertaken at the PEPT Cape Town facility located at iThemba LABS, Cape Town. The steady state motion of media, within a laboratory-scale tumbling mill, was studied for a range of speed and media mixes, using both FNR and PEPT. Several operational parameters were derived from the data, which could be related to potential improvements to the milling efficiency. The blending of FNR and PEPT data for the study of steady state flow, was explored for the first time. In addition, the flow of water through porous media was studied using FNR, which enabled the determination of the hydraulic conductivity, and hence intrinsic permeability, of the media within the column. The potential of using FNR, without or without PEPT, for the study of material in motion is discussed.

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Hasper, Jens. "Systematic study of photoneutron reactions just above the neutron emission threshold /." Phd thesis, München : Verl. Dr. Hut, 2008. http://tuprints.ulb.tu-darmstadt.de/1011/1/Hasper_Systematic_study_of_photoneutron_reactions.pdf.

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This thesis deals with the systematic study of photoneutron reactions in the astrophysically relevant energy region just above the neutron threshold. Photodisintegration reactions play a decisive role in the nucleosynthesis of elements heavier than iron. A large number of proton-rich isotopes are believed to be exclusively produced by a combination of (γ,n), (γ,p) and (γ,α) reactions during supernova explosions in the so-called p process. Astrophysical network calculations of this process have to account for thousands of photodisintegration reaction rates which mainly need to be adopted from theoretical predictions. To test and improve the predictive power of these calculations, it is mandatory to provide reliable experimental data for those reactions which can be studied in the laboratory. Therefore, in the scope of this thesis, the photoneutron reactions of various isotopes have been measured in photoactivation experiments at the superconducting Darmstadt electron linear accelerator S-DALINAC. In particular, for the first time, experimental data have been provided for the photoneutron cross sections of rare-earth isotopes in the astrophysically relevant energy region. The experimental results will be compared with theoretical predictions of two statistical model codes and discussed with regard to their astrophysical implications.

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Valenzano, Michael Peter. "Neutron measurements in the vicinity of a self-shielded PET cyclotron." Thesis, Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/17574.

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22

Eriksson, Jacob. "Neutron Emission Spectrometry for Fusion Reactor Diagnosis : Method Development and Data Analysis." Doctoral thesis, Uppsala universitet, Tillämpad kärnfysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-247994.

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It is possible to obtain information about various properties of the fuel ions deuterium (D) and tritium (T) in a fusion plasma by measuring the neutron emission from the plasma. Neutrons are produced in fusion reactions between the fuel ions, which means that the intensity and energy spectrum of the emitted neutrons are related to the densities and velocity distributions of these ions. This thesis describes different methods for analyzing data from fusion neutron measurements. The main focus is on neutron spectrometry measurements, using data used collected at the tokamak fusion reactor JET in England. Several neutron spectrometers are installed at JET, including the time-of-flight spectrometer TOFOR and the magnetic proton recoil (MPRu) spectrometer. Part of the work is concerned with the calculation of neutron spectra from given fuel ion distributions. Most fusion reactions of interest – such as the D + T and D + D reactions – have two particles in the final state, but there are also examples where three particles are produced, e.g. in the T + T reaction. Both two- and three-body reactions are considered in this thesis. A method for including the finite Larmor radii of the fuel ions in the spectrum calculation is also developed. This effect was seen to significantly affect the shape of the measured TOFOR spectrum for a plasma scenario utilizing ion cyclotron resonance heating (ICRH) in combination with neutral beam injection (NBI). Using the capability to calculate neutron spectra, it is possible to set up different parametric models of the neutron emission for various plasma scenarios. In this thesis, such models are used to estimate the fuel ion density in NBI heated plasmas and the fast D distribution in plasmas with ICRH.

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Olsson, Fredrik. "Estimating the fuel ion dilution in fusion plasmas using neutron emission spectrometry." Thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-227653.

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Fusion power has the potential to produce clean and safe energy that can contribute significantly to the worlds energy system. The road to this promising energy resource has been long, but with one of the biggest projects in the scientific area that is now on going, a fusion project called ITER, the end of the road is ahead of us. Experiments with a new reactor wall are now in progress at the fusion test reactor JET in Oxford, England. The experiment is a pre study of a possible reactor wall for the new fusion reactor ITER in Cadarache in Provence-Alpes-Côte-d'Azur, France. The ITER like reactor wall (ILW) contains Beryllium and has theoretically favourable properties for achieving better reactor conditions, compared to the old Carbon based wall (CW). One reason for changing the wall is to decrease the fuel dilution, i.e. amount of particles that the reactor wall contributes to the fusion plasma. This is an important factor to minimize; 1% of fuel dilution with Carbon will cause a loss in power up to 12%, while the corresponding value for Beryllium is 8%. For Deuterium fuelled plasmas at JET, the fuel dilution can be quantified by the ratio of the Deuterium and electron densities, nd/ne. In this work, nd/ne is estimated using data from the neutron emission spectrometer TOFOR, along with measurements of the electron density (ne) and temperature (Te). In this report it is investigated how sensitive these fuel dilution measurements are to uncertainties in the measurements of ne and Te. The fuel dilution measurements changed relatively in a span of 10% to 23% when changing Te and ne with 10% in the fuel dilution model. To determine the differences in fuel dilution between the Carbon and ITER like reactor wall, a comparison has to be made between the old reactor wall and the new ILW. To do this, similar plasma scenarios need to be represented during fusion discharges with both walls. In this report, JET’s database is searched through using different search criteria, in order to enable a fair comparison between the walls. The comparison showed a tendency of lower fuel dilution, i.e. cleaner plasmas, for discharges with the ILW, but the data points are quite scattered and the ILW discharges have, in general, a lower temperature than the CW discharges, which makes the comparison difficult. Therefore, it is too early to definitely tell anything about a possible improvement of the fuel dilution levels after the installation of the ILW.

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Tardocchi, Marco. "Neutron emission spectroscopy studies of fusion plasmas of Deuterium-Tritium in Tokamaks /." Uppsala : Suède : Acta Universitatis Upsaliensis, 2000. http://catalogue.bnf.fr/ark:/12148/cb40206623k.

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Binda, Federico. "Neutron emission spectroscopy of fusion plasmas with a NE213 liquid scintillator at JET." Licentiate thesis, Uppsala universitet, Tillämpad kärnfysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-291506.

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Neutron diagnostics will play a fundamental role in future fusion plasma machines,where the harsh environment will make the use of many other type of diagnos-tics practically impossible. Complex techniques to measure the neutron spectrumemitted from tokamk plasmas have been developed over the years, producing stateof the art neutron spectrometers. However, recently compact neutron spectrom-eters have been gaining the interest of the research community. They are muchsimpler to operate and maintain, have lower cost and they can be employed in thechannels of a neutron camera, providing profile measurements. The drawbacks arethat they have a worse resolution and a response to neutrons that is not optimalfor spectroscopy.The goal of the work presented in this thesis is to estimate to which extenta compact detector such as a NE213 liquid scintillator can be used to performneutron emission spectroscopy analysis.The detector used for this study was installed in the back of the MPRu spec-trometer at JET in 2012. The characterization of the response of the detector wasdone using a combination of MCNPX simulations and real measurements. Thedata analysis was performed using the forward fitting approach: a model of theneutron spectrum is produced, then folded with the response of the detector andfinally compared with the data. Two types of plasma scenarios were analyzed, onewith NBI heating only, and another with NBI and third harmonic radio-frequencyheating. In both cases the TOFOR spectrometer was used as a reference to esti-mate the parameters in the model of the neutron spectrum.The results are promising and suggest that neutron spectroscopy can be per-formed with NE213 scintillators although the quality of the results, as given byperformance indicators such as uncertainties, is much lower than the performanceof high resolution spectrometers.

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Davies, Glyn. "Emission tomography in the determination of the spatial distribution of neutron induced radionuclides." Thesis, University of Surrey, 1989. http://epubs.surrey.ac.uk/847355/.

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Work has been carried out to investigate the applicability of Neutron Induced Emission Tomography (NIET) to areas of non-destructive testing within the nuclear industry. The principal application was the scanning of irradiated nuclear fuel rods. In addition to its medical uses, tomography has been employed in many areas of non-destructive testing. However, the applications have generally used transmission tomography to examine structure. NIET provides a method of determining the spatial distribution of radionuclides produced by the action of neutrons by activation or fission processes. This has applications as an extension of neutron activation analysis and as a method of non-destructive testing for use in the nuclear industry. The work has involved the use of a number of experimental tomography scanners. Various test objects have been scanned using both emission and transmission tomography and computer programs were developed to collect, process and reconstruct the data. High resolution detectors were used to scan single and multi-energetic radionuclides in test objects designed to model various characteristics of nuclear fuel rods. The effects of scattering on image quality were examined and a method of scattering correction based upon the use of an additional energy window was applied. The work showed the viability of using NIET to study the distribution of radionuclides within objects such as irradiated fuel pellets. It also demonstrated the need for reducing the scattering component within images. The use of narrow energy windows and a high resolution detector were shown to be succesful in reducing the effects of scattering. The employment of scattering correction using additional energy windows was shown to be necessary when scanning multi-energetic radionuclides.

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NOCENTE, MASSIMO. "Neutron and gamma-ray emission spectroscopy as fast ion diagnostics in fusion plasmas." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2012. http://hdl.handle.net/10281/28397.

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This thesis work addresses neutron and γ-ray emission spectroscopy as fast ion diagnostics for fusion plasmas. Two main topics are considered. The first one is the determination of the fast ion energy distribution from measured neutron and γ-ray emission spectra. Neutron spectroscopy has been used at the JET tokamak since 1984. Advanced spectrometers have been built and several features of the neutron emission spectrum have been measured and interpreted in terms of the reaction kinematics. This thesis adds to this knowledge base by inspecting the role of nuclear elastic scattering in producing high energy components in the spectrum from fusion neutrons. The analysis focuses on the possibility to determine the energy distribution tail temperature of radio- frequency heated 3He ions in deuterium plasmas with an admixture of 3He. The RF generation of fast 3He ions is described and the knock-on components are determined with the help of newly derived 3He +d scattering cross sections. Results are presented on the neutron emission spectrum and its contributions from different deuteron velocity components. It is shown that knock-on leaves an observable feature in the spectrum with a clear dependence on absorbed RF power. The investigation is then generalized to D, (3He)D, DT and (3He)DT plasmas, where the relative magnitude of nuclear elastic scattering from different fusion products is determined. The resulting signatures in the neutron emission spectrum are calculated and their relevance for fast ions diagnosis in a burning plasma experiment is discussed. Gamma-ray spectroscopy is a relatively new technique compared to neutron spectroscopy. The Doppler broadening of characteristic γ-ray emission peaks from 12C(3He, pγ)14N reactions in fusion plasmas was measured for the first time in 2008 at the JET tokamak thanks to the installation of a High Purity Germanium detector. In this thesis, intensities and detailed spectral shapes of γ-ray emission peaks are successfully reproduced using a physics model combining the kinetics of the reacting ions with a detailed description of the nuclear reaction differential cross sections for populating the L1-L8 14N excitation levels yielding the observed γ-ray emission. A Monte Carlo code, named GENESIS, was written for the purpose of interpreting γ-ray emission from fusion plasmas and is used here to determine the tail temperature of fast 3He ions from the observed peak shapes. Experiments performed in 4He plasmas of the JET tokamak are also presented. 4He ions were accelerated to the MeV range by coupling third harmonic radio frequency heating to an injected 4He beam. For the first time, Doppler broadening of γ-ray peaks from the 12C(d, pγ)13 C and 9Be(α, nγ)12 C reactions was observed and is here interpreted with the GENESIS code. Acceleration of 4He particles at energies as high as 6 MeV is demonstrated; implications of these results for α particle observations through γ-ray emission spectroscopy in next step deuterium-tritium plasmas are discussed. A second topic addressed by this work is the study of fast ion driven instabilities through γ-ray emission spectroscopy, with emphasis on the development of instrumentation. A high efficiency, high resolution, fast γ-ray spectrometer based on the LaBr3 scintillator and designed for measurements in the MHz range was developed and is here presented. An algorithm based on pulse shape fitting was written to reconstruct γ-ray spectra from digitized data and is shown to provide an energy resolution equivalent to a traditional analog spectrometry chain at low counting rates. The same system was used to perform γ-ray spectroscopy in the MHz range, as demonstrated in experiments performed at nuclear accelerators. γ-ray emission spectra at rates as high as 4 MHz from p + 27Al reactions collected at the Tandem Van der Graaf accelerator of the Nuclear Institute “Horia Hulubei“ (Magurele, RO) are presented and show little or no degradation of the energy resolution. The developed system was also employed to study instabilities driven by fast protons in the ASDEX Upgrade tokamak. The observed γ-ray emission level induced by energetic protons is used to determine an effective tail temperature of the proton distribution function that can be compared with Neutral Particle Analyzer measurements. More generally the measured emission rate is used to assess the confinement of protons with energies less than 400 keV in discharges affected by Toroidal Alfven Eigenmode instabilities. The derived information on confined ions is combined with observations made with the ASDEX Upgrade Fast Ion Loss Detector. The results presented in this thesis represent a step forward in the development of nuclear radiation based methods for burning plasma diagnostics. In particular, they demonstrate that quantitative information on the energy distribution of fast ions and their interaction with plasma instabilities can be inferred from neutron and γ-ray mea- surements by taking into account in detail the reaction processes contributing to the emission of nuclear radiation from the plasma.

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Hime, Andrew. "Heavy neutrino emission in nuclear beta decay spectra." Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293432.

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Tavares, Leonardo Estêvão Schendes. "Tomography of the Earth by Geo-Neutrino Emission." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-02102014-121344/.

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Geo-neutrinos are electronic anti-neutrinos originated from the beta decay process of some few elements in the decay chains of $^Th$ and $^U$ present in Earth\'s interior. Recent experimental measurements of these particles have been generating great expectations towards a new way for investigating directly the interior of the planet. It is a new multidisciplinary area, which might in the near future bring considerable clues about Earth\'s thermal dynamics and formation processes. In this work, we construct an inferential model based on the multigrid priors method to deal, in a generic way, with the geo-neutrino source reconstruction problem. It is an inverse problem; given a region in space V and a finite and small number of measurements of the potential generated on the surface of V by some charge distribution $ho$, we try to infer $ho$. We present examples of applications and analysis of models in two and three dimensions and we also comment how other a priori information may be included. Furthermore, we indicate the steps for inferring the best locations for future detectors. The objective is to maximize the amount of information liable to be obtained from experimental measurements. We resort to an entropic method of inference which may be applied right after the results of the multigrid method are obtained.
Geo-neutrinos são neutrinos provindos do decaimento beta de alguns poucos elementos nas cadeias de $^$Th e $^$U presentes no interior da Terra. Recentes medidas experimentais dessas partículas têm proporcionado grandes expectativas como uma nova maneira de se investigar o interior do planeta diretamente. Trata-se de uma área multidisciplinar nova, que poderá no futuro próximo nos trazer grandes esclarecimentos sobre a dinâmica térmica e o processo de formação da Terra. Neste trabalho, construímos um modelo de inferência baseado no método de multigrid de priors para tratar, de modo genérico, o problema da reconstrução das fontes de geo-neutrinos no interior da Terra. Trata-se de um problema inverso; dada uma região do espaço V e um número finito e pequeno de medidas do potencial gerado na superfície de V por uma distribuição de carga $ho$, tentamos inferir $ho$. Apresentamos exemplos de aplicações e análises do método em modelos bidimensionais e tridimensionais e também comentamos como outras informações a priori podem ser incorporadas. Além disso, indicamos os passos para se inferir onde detectores futuros devem ser posicionados. O objetivo é maximizar a informação passível de ser obtida das medidas experimentais. Utilizamos um método baseado em inferência entrópica e que pode ser aplicado diretamente depois que os resultados do método de multigrid são obtidos.

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TARDELLI, TIAGO C. "Avaliação de dados nucleares para dosimetria de nêutrons." reponame:Repositório Institucional do IPEN, 2013. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10587.

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Made available in DSpace on 2014-10-09T14:05:21Z (GMT). No. of bitstreams: 0
Dissertação (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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Lin, Yawei. "Spectroscopy of High Energy Ion-neutral Collisions." Thesis, Université d'Ottawa / University of Ottawa, 2011. http://hdl.handle.net/10393/19720.

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This research work focused on studying the emission spectroscopy produced from the high energy ion-molecule collision processes in mass spectrometry. The collision experiments are described and divided into 4 chapters (Chapter 3, 4, 5, 6).N2O+● is an ion of atmospheric importance. In chapter 3 the investigation of the collision between high translational energy (4-8 keV range) N2O+● ions and Helium target gas in mass spectrometry using collision induced emission (CIE) spectroscopy is described.In chapter 4, the collision-induced emission (CIE) spectra from 4-8 keV collisions between projectile He+● ions and CO2 target gas (He+●/CO2) were obtained. In Chapter 5, to probe the validity of this hypothesis, CIE experiments were carried out to observe the photon emissions from keV collisions of a selection of projectile ions with O2 target gas. By studying the resulting CIE spectra, a second potential mechanism came to light, one that involves the nearly isoenergetic O2+. A → X state transition. In chapter 6, neutral hydroxymethylene and formaldehyde were generated by charge exchange neutralization of their respective ionic counterparts and then were reionized and detected as recovery signals in neutralization-reionization mass spectrometry in the modified VG-ZAB mass spectrometer.

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RIGOSELLI, MICHELA. "X-ray emission from the magnetic polar caps of old rotation-powered pulsars." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2020. http://hdl.handle.net/10281/277373.

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Le stelle di neutroni sono il risultato dell'evoluzione di stelle massive dopo l'esplosione di supernova. Il progetto di questa Tesi di PhD consiste nello studio dell'emissione di raggi X da parte di stelle di neutroni isolate di età superiore a 100000 anni. Sono stati analizzati dati provenienti dal satellite XMM-Newton (ESA). Per estrarre la miglior informazione possibile dai dati, ho implementato un metodo di maximum likelihood (ML) e l'ho utilizzato per estrarre spettri e profili pulsati di pulsar vecchie in banda X, che poi sono stati analizzati con raffinati di emissione. La Tesi è strutturata come segue: nei primi tre capitoli illustro le proprietà principali delle stelle di neutroni, con particolare attenzione ai processi termici e non termici che producono raggi X. I raggi X non termici sono prodotti da particelle relativistiche accelerate da campi elettromagnetici; una frazione di queste particelle viene accelerata verso la superficie della stella, e riscalda le zone delle calotte polari magnetiche. La componente termica, che può essere prodotta dall'intera superficie o da una parte, viene solitamente descritta come un corpo nero; tuttavia, la presenza di intensi campi magnetici superficiali influenza le proprietà della materia, e la radiazione emessa è ampiamente anisotropa. Nel Capitolo 4 descrivo come ho generato spettri e profili pulsati sintetici, utilizzando modelli di emissione che considerano calotte polari ricoperte di un'atmosfera di idrogeno magnetizzata. Mi sono basata su un software esistente che, dato un certo set di parametri relativi alle proprietà fisiche della stella, stima l'intensità della radiazione prodotta. Successivamente, esso somma i contributi degli elementi di superficie che sono visibili all'osservatore alle differenti fasi di rotazione. Quindi, nel Capitolo 5 descrivo come ho implementato un software di analisi che si basa sul metodo di ML. Dato un certo modello, esso stima i parametri più probabili che ricostruiscono i dati osservati, nella fattispecie il numero di conteggi relativo alla sorgente e al background. Ho validato il metodo e dimostrato che esso è particolarmente efficace per sorgenti deboli, quali sono la maggior parte delle pulsar vecchie. Successivamente, ho applicato i metodi finora descritti ad alcune pulsar vecchie. Nel Capitolo 6 riporto l'analisi di PSR J0726-2612, una pulsar radio che ha alcune delle caratteristiche delle XDINSs: un periodo di rotazione lungo, un intenso campo magnetico, ed emissione X termica. Grazie ad un'analisi congiunta dello spettro e del profilo pulsato, ho mostrato che la presenza di impulsi radio in PSR J0726-2612, così come la loro assenza nelle XDINSs, potrebbe essere dovuta ad un'orientazione differente rispetto all'osservatore. Nel Capitolo 7 presento il caso di PSR B0943+10, una pulsar con emissione X sia termica sia non termica ma che, nonostante sia un rotatore allineato, ha una grande frazione pulsata. Sono riuscita a riappacificare i due diversi aspetti grazie ad un'attenta analisi di ML e all'intrinseca anisotropia dell'emissione termica prodotta da un'atmosfera magnetizzata. Nel Capitolo 8 ho invece applicato il metodo di ML su sette pulsar poco brillanti, delle quali quattro avevano diverse analisi già pubblicate in letteratura, ma con risultati discordanti, mentre le altre tre non erano ancora state rivelate in banda X. Ho trovato tracce evidenti di emissione termica solo in due oggetti, più un accenno nello spettro pulsato di un terzo oggetto. Infine, ho considerato tutte le pulsar vecchie che emettono raggi X termici e ho confrontato le misure di temperatura, raggio e luminosità alle aspettative dei modelli teorici. In particolare, ho scoperto che le aree di emissione sono generalmente in accordo con quelle previste dal modello di dipolo magnetico rotante, purché vengano considerati anche effetti di proiezione geometrica e modelli di emissione realistici, quali appunto i modelli di atmosfera magnetizzata.
Neutron stars are the remnants of massive stars whose cores collapse during the supernova explosions. The project of this PhD Thesis consisted in the study of the X-ray emission from isolated neutron stars older than about 100000 years. The work was based mainly on data obtained with the XMM-Newton satellite (ESA). To extract the best possible information from the data, I implemented a maximum likelihood (ML) technique and used it to derive the X-ray spectra and pulse profiles of several old pulsars, that were then studied with state-of-the-art models of X-ray emission. The Thesis is structured as follows: in the first three chapters I outline the main properties of neutron stars, with a major focus on the thermal and nonthermal processes that produce X-rays. The nonthermal X-rays are produced by relativistic particles accelerated by rotation-induced electric fields and moving along the magnetic field lines. A fraction of these particles is accelerated backward and returns on the stellar surface, heating the magnetic polar caps. The thermal component, that can be produced by the whole stellar surface or by small hot spots, can be described, in a first approximation, by a blackbody. However, the presence of intense surface magnetic fields strongly affects the properties of matter, and the emergent radiation is widely anisotropic. In Chapter 4, I describe how I generated synthetic spectra and pulse profiles using thermal emission models that consider polar caps covered by a magnetized hydrogen atmosphere or with a condensed iron surface. I relied on an existing software that, given a set of stellar parameters, evaluates the emerging intensity of the radiation. A second software, which I adapted on the sources I analyzed in the Thesis, collects the contribution of surface elements which are in view at different rotation phases from a stationary observer. Then, in Chapter 5, I describe how I implemented an analysis software that relies on the ML method. It estimates the most probable number of source and background counts by comparing the spatial distribution of the observed counts with the expected distribution for a point source plus an uniform background. I demonstrated that the ML method is particularly effective for dim sources, as most old pulsars are. Subsequently, I applied the methods described above to some old pulsars. In Chapter 6, I report the analysis of PSR J0726-2612, a radio pulsars that shares some properties with the radio-silent XDINSs, as the long period, the high magnetic field, and the thermal X-ray emission from the cooling surface. Thanks to an in-depth analysis of the combined spectrum and pulse profile, I showed that the presence of radio pulses from PSR J0726-2612, as well as the absence from the XDINSs, might simply be due to different viewing geometries. In Chapter 7, I present the case of PSR B0943+10, a pulsar with a nonthermal and thermal X-ray spectrum but that, despite being an aligned rotator, has a large pulsed fraction. I could reconcile the two opposite properties analyzing with the ML the spectrum and the pulse profile, and considering the magnetic beaming of a magnetized atmosphere model, that well fits the thermal component. In Chapter 8, I applied the ML method to seven old and dim pulsars, of which four had controversial published results, and three were so far undetected. I found convincing evidence of thermal emission only in the phase-averaged spectrum of two of them, plus a hint for a thermal pulsed spectrum in a third object. Finally, I considered all the old thermal emitters and I compared their observed temperatures, radii and luminosities to the expectations of the current theoretical models for these objects. In particular, I found that the emitting area are generally in agreement with the polar cap regions evaluated in a dipole approximation, if the combined effects of geometry projections plus realistic thermal models (as the magnetic atmosphere) are taken into account.

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Diniz, Gabriel Sousa. "High energy emissions from thunderstorms: HEETs, from photons to neutrons toward the ground." Instituto Nacional de Pesquisas Espaciais (INPE), 2016. http://urlib.net/sid.inpe.br/mtc-m21b/2016/02.04.22.21.

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Thunderstorms are the starting point of several intense phenomena such as gamma rays and X rays, neutron, positron and electron emissions. The X rays and gamma rays have energies that may reach 100 MeV. The neutron emissions may be created by energetic gamma ray photons interacting with the air via Giant Dipole Resonance, a photonuclear reaction, related to thunderstorms and lightning in a way that is not completely understood yet. In this work neutrons were assumed to be created by gamma ray photons in the energy range of 10-30 MeV emitted by leader discharges. Their production and propagation toward the ground were investigated using computer simulations. Cross sections data banks were analyzed to provide estimations on the neutrons creation probability. The analysis revealed that the probability per collision of a photonuclear occurs varies between 0 and 3.2\% through the energy range of 10 and 30 MeV. The photons mean free path within this energy range was analyzed together with the atmospheric density profile showing that for photon source altitudes above 1 km, the photons with this energy pass through a sufficiently high number of mean free path to ensure a collision. The free software EGS5 was used to treat the photons and electrons motion through the atmosphere in the intent of analyze the spread of the beams, that were assumed to be monodirectional. The photon beam presented an aperture of 2-6$^{o}$ $\pm$ 2$^{o}$ while the electron beam was broader showing an aperture of 11-13$^{o}$ $\pm$ 3$^{o}$. Since EGS5 does not take into account neutron production and motion, the neutron analysis was done with the FLUKA software simulating a photon beam in different initial heights and estimating the photon and neutron ground detection. FLUKA simulations have shown that neutrons are distributed at the ground within a radius of 2 km away from the source axis. The neutrons reached ground with a rate of 10$^{-4} $-10$^{-2}$ neutrons per gamma, which agrees with the cross section analysis done upon the neutron production. The neutron number decrease was used to estimate an upper limit of 5 km for the altitude of a punctual photon source that is capable of generating ground detectable neutrons.
Nuvens de tempestade são o início de vários fenômenos intensos como os raios gama e raios X, bem como de emissões de nêutrons, pósitrons e elétrons. As emissões de raios X e raios gama possuem energias que alcançam 100 MeV. As emissões de nêutrons podem ser criadas por interações entre raios gamma com o ar através da Ressonância Gigante de Dipolo, uma reação foto-nuclear, relacionadas com as nuvens de tempestade e com raios de um modo ainda não totalmente compreendido. Neste trabalho supõe-se que os nêutrons são criados por fótons de raios gamma com energia entre 10-30 MeV emitidos durante a propagação do líder negativo. A produção e a propagação pelo ar destes nêutrons foram investigadas utilizando simulações computacionais. Bancos de dados de seções de choque foram analisados para estimar a probabilidade por colisão de uma reação foto-nuclear acontecer. A análise revelou que essa probabilidade varia entre 0\% e 3.2\% para fótons com energia entre 10 e 30 MeV. O livre caminho médio dos fótons no intervalo de energia de 10-30 MeV foi analisado junto com o perfil de densidade atmosférica. A análise mostrou que para fótons com altitude inicial acima de 1 km, eles passam por livres caminhos médios o suficiente para a probabilidade de ocorrência de ao menos uma colisão ser garantida. O software livre EGS5 baseado no método Monte Carlo foi usado para tratar o movimento dos fótons e elétrons pela atmosfera no intuito de estudar a difusão de feixes monodirecionais dessas partículas. Foi observado que o feixe de fótons possui uma abertura entre 2-6$^{o}$ $\pm$ 2$^{o}$ enquanto o feixe de elétrons possui uma abertura de 11-13$^{o}$ $\pm$ 3$^{o}$ . A análise de nêutrons foi feita com o software FLUKA simulando um feixe de fótons em diferentes altitudes iniciais e estimando a detecção de fótons e nêutrons no solo. As simulações do FLUKA mostraram que os nêutrons se distribuem no solo em uma distância radial da fonte de 2 km, chegando ao solo numa razão entre 10$^{-4}$ até 10$^{-2}$ nêutrons/fótons, o que concorda com a análise das seções de choque. A diminuição dos nêutrons detectados em solo permitiu a estimativa de uma altura limite de 5 km para uma fonte pontual de fótons capaz de produzir nêutrons detectáveis em solo.

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Skiba, Mateusz. "Making TOFu : Fusion Plasma Neutron Emission Spectrometry with a Fully Digital Data Acquisition System." Doctoral thesis, Uppsala universitet, Tillämpad kärnfysik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-304383.

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TOFu (Time-Of-Flight upgrade) is a fully digital data acquisition system based on 1 GSPS, 12 bit digitisers for the TOFOR (Time-Of-Flight spectrometer Optimised for Rate) fusion neutron spectrometer at JET. The system has been assessed, developed and subsequently tested during experimental campaigns at JET. A detailed presentation is provided, describing the electronics setup, as well as solutions to challenges related to time-alignment and synchronisation of the signal lines and digitisers. The system enables kinematic discrimination of spectral background, based on associated time and energy measurements. This technique has been tested with synthetic data, evaluated, and compared to experimental results. The kinematic background discrimination method is shown to provide improvements in signal-to-background ratio of up to 500 % in certain spectral regions. TOFOR is optimised for spectrometry of deuterium-deuterium fusion neutron emission at JET. The primary purpose of TOFu is to enable TOFOR to retain these spectrometric capabilities in the presence of a strong background of high-energy deuterium-tritium fusion emission neutrons, in a forthcoming deuterium-tritium fusion plasma campaign at JET. However, the improvement in signal-to-background ratio also allows for detailed studies of low-intensity spectral components, such as the contribution due to neutrons scattering off the internal wall of the JET tokamak before impinging on the TOFOR sight line. Satisfying experimental results pertaining to this aspect of spectral analysis with TOFu data are shown. Finally, a conceptual backscattering time-of-flight spectrometer, based on deuterated scintillator detectors is presented. The backscattering time-of-flight technique is shown to be able to provide high-resolution spectrometric capabilities of deuterium-tritium fusion plasma neutron emission. Studies with synthetic data are used to demonstrate these capabilities and the effects of the developed background discrimination techniques on deuterium-tritium fusion neutron spectra obtained with the instrument.

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Olivo, Martino. "Neutrino emission from high-energy component gamma-ray bursts." Licentiate thesis, Uppsala universitet, Högenergifysik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-132961.

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Gamma-ray bursts (GRBs) are brief and sudden explosions radiating most of their energy in the soft γ-ray band ( 100 keV). In the context of multimessenger astroparticle physics recent observations of GRBs provide an excellent benchmark for testing theoretical models of high energy emission mechanisms. Acceleration of hadrons in the engine is expected to produce high energy neutrinos and gamma-rays simultaneously via π±/π0 decays, thus reinforcing the motivation for coincident searches in km3 neutrino telescopes. The Waxman-Bachall spectra and the corresponding expected neutrino rates in IceCube are derived here for GRB090510 amd GRB090902B recently detected by the Fermi Large Area Telescope. The implications of the significant detection of deviations from the Band function fit in photon spectra and a model that explains these extra-components in terms of π0-decay photons are presented here and the relevance to neutrino astronomy is shown.

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Raab, Christoph. "Searches for Neutrino Emission from Blazar Flares with IceCube." Doctoral thesis, Universite Libre de Bruxelles, 2021. https://dipot.ulb.ac.be/dspace/bitstream/2013/325215/3/toc.pdf.

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Cosmic rays reach Earth from beyond the Milky Way and with energies up to 10^20 eV.The responsible accelerators have to date not been discovered. However, multi-messenger astronomy can shed light on the question, based on the principle that protons and nuclei accelerated in dense and energetic environments would also produce gamma rays and neutrinos. Such environments may be found in "blazars", which are therefore cosmic ray accelerator candidates. Their gamma-ray emission has been observed to increase, sometimes by orders of magnitude, during "flares" as observed in light curves taken by the Large Angle Telescope on the Fermi satellite. When the latter was launched in 2008, the IceCube Neutrino Observatory had also started taking data, detecting the Cherenkov light from high-energy neutrino interactions in the glacier ice under the geographic South Pole. These two experiments have enabled multi-messenger searches for neutrinos in time correlation with the gamma-ray emission from blazars. This work builds on this principle and extends it by "stacking" the signal from multiple blazar flares. Thus, their individually undetectable neutrino emission could still be discoverable. One first analysis focused on the blazar TXS 0506+056, whose flare in 2017 coincided with arrival of the neutrino IceCube-170922A. Extending into a lower energy range than the alert, the search found no additional excess neutrinos associated with the flare. A second analysis used 179 bright and variable blazars. They were divided in two specific blazar classes and weighted relatively to each other, with two weighting schemes motivated physically using the observed gamma-ray luminosity and a third, generic weighting to cover unconsidered scenarios. No significant neutrino excess was found in the unblinded likelihood fits for any of the source catalogues and weighting schemes. Their combined trial-corrected p-value was p=(79.1 +/- 0.3)%. The limits derived from this analysis are also discussed and its relation with other searches considered. Since that was the first "blazar flare stacking", this work also proposes further improvements to the analysis which will help advance the search for cosmic ray accelerators.
Les rayons cosmiques proviennent d'au-delà de la Voie lactée et atteignent la Terre avec des énergies pouvant aller jusqu'à 10^20 eV. Les objets qui accélèrent ces rayons cosmiques n'ont toujours pas été découverts. Toutefois, l'astronomie multimessager peut apporter un élément de réponse à cette question, en supposant que les protons et les noyaux accélérés dans des environnements denses et énergétiques pourraient également produire des rayons gamma et des neutrinos. Les "blazars" sont de possibles candidats pour les accélérateurs de rayons cosmiques. Une augmentation de leurs émissions de rayons gamma, parfois de plusieurs ordres de grandeur, a été observée lors de phénomènes qu'on appelle "éruption", comme le montrent les courbes de lumière prises par le télescope spatial Fermi-LAT. Lorsque ce dernier a été lancé en 2008, l'observatoire de neutrinos IceCube avait également commencé à prendre des données, détectant la lumière Tcherenkov provenant d'interactions de neutrinos à haute énergie dans la glace qui se trouve sous le Pôle Sud géographique. Ces deux expériences ont permis de mener à bien des recherches multi-messagers de neutrinos en corrélation temporelle avec l'émission de rayons gamma des blazars. Ce principe est le point de départ de cette thèse, qui va plus loin en employant la méthode du "stacking", qui consiste à combiner les signaux provenant de plusieurs éruptions de blazars. Ainsi, leurs émissions individuelles de neutrinos, habituellement indétectables, pourraient être découvertes après combinaison. Une première analyse s'est concentrée sur le blazar TXS 0506+056, dont l'éruption en 2017 a coïncidée avec l'arrivée de l'évènement IceCube-170922A. En considérant une gamme d'énergie inférieure à celle de l'alerte 170922-A, pas d’autres neutrino excédentaire n’a été associé à l'éruption. Une deuxième analyse est basée sur 179 blazars lumineux et variables. Ces blazars ont été répartis en deux classes spécifiques, et chacun d'entre eux a reçu un poids relatif. Trois schémas de pondération ont été considérés :les deux premiers étant motivés par des observations, le troisième étant plus générique. Aucun excès significatif de neutrinos n'a été observé après avoir effectué des ajustements par maximum de vraisemblance sur les données non masquées, pour les différents catalogues de sources et schémas de pondération. Leur valeur-p combinée est de p=(79.1 +/- 0.3)%. Les limites dérivées de cette analyse sont discutées ainsi que leur rapport avec les résultats d'autres recherches. Puisqu'il s'agit du premier stacking d'éruptions de blazars, nous suggérons également des améliorations à apporter à l'analyse afin de permettre la poursuivre de la recherche d'accélérateurs de rayons cosmiques.
Kosmische straling afkomstig van buiten de Melkweg bereikt de Aarde met energieën tot wel 10^20 eV. De astrofysische bronnen waarin deze deeltjes worden versneld zijn tot op heden nog niet ontdekt. De multi-boodschapperastronomie kan een nieuw licht werpen op de oorsprong van kosmische straling, aangezien protonen en atoomkernen die worden versneld in een dichte en energetische omgeving ook gammastralen en neutrino’s produceren. „Blazars” zijn mogelijke kandidaat-versnellers. Observaties van blazars, gemaakt met de ruimtetelescoop Fermi-LAT ,tonen aan dat hun gammastraling tijdens zogenaamde „flakkers” toeneemt. Rond de tijd dat deze werd gelanceerd, begon het IceCube Neutrino Observatorium ook gegevens te verzamelen. Deze laatste detecteert hoog-energetische neutrino’s aan de hand van het Cherenkovlicht dat geproduceerd wordt tijdens hun interacties met de ijskap bij de geografische zuidpool. Deze twee experimenten hebben het mogelijk gemaakt om een multibooschapperzoektocht te verrichten naar neutrino’s van blazars die een tijdscorrelatie hebben met diens flakkers van gammastraling. Dit is het uitgangspunt van dit proefschrift, waarbij er ook een zogenaamde „stapelmethode” wordt toegepast. Op deze manier kan de neutrino-emissie van indivuele blazarflakkers, die afzonderlijk te zwak is om te detecteren, gecombineerd worden en mogelijks toch worden ontdekt. Een eerste analyse legt de focus op de blazar TXS 0506+056, waarvan een flakker in 2017 samenviel met de aankomst van het neutrino IceCube 170922-A. In een relatief lager energiebereik wordt er geen surplus aan neutrino’s gevonden gecorreleerd met de flakker. In een tweede analyse maken we gebruik van de stapelmethode om neutrino’s te zoeken afkomstig van 179 heldere en variabale blazars. Deze worden onderverdeeld in twee specifieke klassen en krijgen elks een zeker gewicht in de stapelanalyse. Hiervoor worden twee wegingsschema’s gebruikt die gemotiveerd zijn door de geobserveerde gammastraling, alsook een derde generieke weging. Ook hierwordt er geen significant neutrinosignaal geobserveerd. De gecombineerde p waarde is p=(79.1 +/- 0.3)%. Hieruit worden limieten afgeleid, en worden de verbanden met andere zoekacties besproken. Aangezien dit werk de eerste analyse omvat naar neutrino’s afkomstig van blazarflakkers gebruik makende van een stapelmethode, worden er in dit werk ook verdere verbeteringen van de analyse voorgesteld. Deze zullen als een startpunt dienen voor toekomstige zoektochten naar de nog onbekende bronnen van kosmische straling.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished

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37

O'Rourke, Brogan Roisín. "AGN Candidates for High Energy Neutrino Emission in IceCube." Thesis, Uppsala universitet, Högenergifysik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-409739.

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Since the construction of the IceCube Neutrino Observatory was completed in 2010, many amazing discoveries have been made in the field of neutrino physics. Recently a neutrino event has been linked to an blazar-type active galactic nucleus source, bringing us one step closer to understanding the production of high-energy extragalactic neutrinos and ushering in a new era of multimessenger astronomy. This was found by linking the neutrino event to one of the Fermi Collaboration’s gamma ray sources which had a blazar counterpart. The quest to link other neutrino events to AGN (active galactic nuclei) sources through collaboration with the Fermi Large Area Telescope has turned up some interesting candidates. The fact that some of these potential sources are not blazars is curious and, although unconfirmed as neutrino sources, these objects merit further investigation due to their unusual nature.

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CAVALIERI, TASSIO A. "Emprego do NCNP no estudo dos TLDs 600 e 700 visando a implementação da caracterização do feixe de irradiação na instalação de BNCT do IEA-R1." reponame:Repositório Institucional do IPEN, 2013. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10565.

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Made available in DSpace on 2014-10-09T12:42:01Z (GMT). No. of bitstreams: 0
Made available in DSpace on 2014-10-09T14:04:33Z (GMT). No. of bitstreams: 1 19174.pdf: 31751 bytes, checksum: 7f1e1ac2bd5fcea7b8edbb1e6ba7a12b (MD5)
Dissertação (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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Trinh, Ngoc Duy. "Emission de neutrons par les réactions d'ions lourds (4,6-95 MeV/nucléon)." Thesis, Normandie, 2018. http://www.theses.fr/2018NORMC234/document.

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Les accélérateurs d’ions lourds sont un outil incontournable pour la recherche en physique nucléaire. Ils sont également utilisés pour diverses applications. Il est nécessaire de caractériser la production des neutrons secondaires dans les accélérateurs afin de garantir un fonctionnement sûr en toutes circonstances. Cependant, les données expérimentales sont très rares voire inexistantes. Pour certaines données, on note des divergences entre différentes publications. Des désaccords sont aussi observés entre les mesures et les calculs. Toutes ces raisons justifient le programme Thick Target Neutron Yields (TTNY) dont l’objectif est de mesurer des spectres doublement différentiels (énergie, angle) des neutrons générés par l’interaction des ions lourds (12≤Afaisceau≤208 et 4,6 MeV/nucléon≤Efaisceau≤95 MeV/nucléon) sur cibles épaisses (natC, natCu et natNb). Deux techniques de mesure ont été utilisées : Activation et Temps de vol. Cela permet d’avoir une meilleure confiance dans les mesures, d’étudier les limites expérimentales et de consolider les conclusions que l’on peut en tirer. Les mesures sont comparées à des simulations effectuées dans ce travail avec les codes Monte-Carlo les plus utilisés en calcul nucléaires : PHITS (japonais), FLUKA (européen (CERN/INFN)) et MCNP (américain). Ces comparaisons ont permis d’évaluer la qualité des codes dans les énergies étudiées et pour les masses des noyaux explorées. Elles ont permis aussi de conclure sur les incertitudes systématiques et les éventuelles évolutions à apporter aux modèles physiques de ces codes
Heavy-ion accelerators are an essential tool for nuclear physics research. They are also adopted in several applications. It is necessary to characterize the secondary neutrons production in order to guarantee a safe operation in every circumstance in accelerators. However, experimental data are very rare or even non-existent. For some data, we notice disagreements between different publications. Disagreements are also observed between measurements data and simulations. For all these reasons, we established the program Thick Target Neutron Yields (TTNY). This program aims to measure the double differential neutron spectra (energy, angle) generated by the interactions of heavy-ions (12≤Abeam≤208 and 4.6 MeV/nucleon≤Ebeam≤95 MeV/nucleon) on thick targets (natC, natCu and natNb). Two measurements methods were adopted: Activation and Time of Flight. This choice allows having a better confidence on the measurements, studying experimental limits and consolidating the conclusions that could be drawn from the experimental results. The measurements are compared to the simulations performed with some Monte-Carlo widely used in nuclear simulation: PHITS (Japanese), FLUKA (European (CERN/INFN)) and MCNP (American). These comparisons allowed evaluating the modeling quality of heavy-ion reactions for the energies and masses explored in this work. We also conclude on the systematic uncertainties and on the potential improvements to be introduced to physics models of these codes

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40

Reed, Alan Thomas. "Decay studies of neutron-rich nuclei." Thesis, University of Liverpool, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367175.

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41

Eriksson, Jacob. "Fuel ion densities and distributions in fusion plasmas : Modeling and analysis for neutron emission spectrometry." Licentiate thesis, Uppsala universitet, Tillämpad kärnfysik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-192530.

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Neutrons produced in fusion reactions in a magnetically confined plasma carry information about the distributions and densities of the fuel ions in the plasma. This thesis presents work where various theoretical models of different fuel ion distributions in the plasma are used to calculate modeled components of the neutron energy spectrum. The calculated components can then be compared with measured data, either to benchmark and validate the model or to derive various plasma parameters from the experimental data. Neutron spectra measured with the spectrometers TOFOR and the MPR, which are both installed at the JET tokamak in England, are used for this purpose. The thesis is based on three papers. The first paper presents the analysis of TOFOR data from plasmas heated with neutral beams and radio frequency waves tuned to the third harmonic of the deuterium cyclotron frequency, which creates fast (supra thermal) ions in the MeV range. It is found that effects of the finite Larmor radii of the fast ions need to be included in the modeling in order to understand the data. These effects are important for fast ion measurements if there is a gradient in the fast ion distribution function with a scale length that is comparable to - or smaller than - the width of the field of view of the measuring instrument, and if this scale length is comparable to - or smaller than - the Larmor radii of the fast ions. The second paper presents calculations of the neutron energy spectrum from the T(t,n)4He reaction, for JET relevant fuel ion distributions. This is to to form a starting point for the investigation of the possibility to obtain fast ion information from the t-t neutron spectrum, in a possible future deuterium-tritium campaign at JET. The t-t spectrum is more challenging to analyze than the d-d and d-t cases, since this reaction has three (rather than two) particles in the final state, which results in a broad continuum of neutron energies rather than a peak. However, the presence of various final state interactions - in particular between the neutron and the 4He - might still allow for spectrometry analysis. Finally, in Paper III, a method to derive the fuel ion ratio, nt/nd, is presented and applied to MPR data from the JET d-t campaign in 1997. The trend in the results are consistent with Penning trap measurements of the fuel ion ratio at the plasma edge, but the absolute numbers are not the same. Measuring the fuel ion ratio in the core plasma is an important task for fusion research, and also a very complicated one. Future work should aim at measuring this quantity in several independent ways, which should then be cross checked against each other.

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Giacomelli, Luca. "Development of Neutron Emission Spectroscopy Instrumentation for Deuterium and Deuterium-Tritium Fusion Plasmas at JET." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8199.

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43

Henriksson, Hans. "Neutron Spectroscopy Studies of Heating Effects in Fusion Plasmas." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-3492.

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44

Nchodu, M. R. "Alpha emission from the interactions of 14-200 MeV neutrons on carbon-12." Master's thesis, University of Cape Town, 1994. http://hdl.handle.net/11427/17513.

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Summary in English.
Bibliography: pages 89-93.
Cross-sections for the production of alpha particles from the ¹²C(n,α)⁹Begs and ¹²C(n,n')3α reactions were measured for incident neutrons in the energy range 25 to 52 MeV. The measurements were reduced to absolute cross-sections by simultaneously observing deuteron recoils from n-d elastic scattering in the scintillator using D(n,n)D elastic scattering cross-section as a reference standard. Neutron energy was determined by time-of-flight and pulse shape discrimination (PSD) was used to identify and separate alphas and deuterons from other reaction products. The feasibility of distinguishing different mechanisms for the ¹²C(n,n')3α reaction by means of PSD was also investigated.

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45

Testov, Dmitry. "Effect of shell closure N = 50 and N = 82 on the structure of very neutron-rich nuclei produced at ALTO : measurements of neutron emission probabilities and half lives of nuclei at astrophysical r-processes path." Phd thesis, Université Paris Sud - Paris XI, 2014. http://tel.archives-ouvertes.fr/tel-01059803.

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Nowadays we are all witnesses of a competition of facilities at different countries to study unknown regions of neutron rich nuclei. Much efforts are devoted to understand the role of neutron excess and its influence on nuclei in vicinity of closed neutron shells. One of the means to investigate nuclear structure is in beta-decay. Once a nucleus is proven to exist, its beta-decay properties, such as T1/2 and Pn (probability of beta-delayed neutron emission), which are relatively easy to measure, can provide the first hints on the nuclear structure. On the r-process site, "waiting points"(nuclei on closed neutron shells) has significant effects on the r-process dynamics and the abundance distribution. The actual side and the astrophysical conditions under which the nuclear synthesis takes place are still not certainly known - since r-process nuclei are difficult to produce and to study experimentally, input parameters for r-process calculations are mostly derived from theoretical models. As it has been seen lately, most of the theories have failed to reproduce newly measured data sets near shell closures. With new experimental data already (or shortly) available theoretical approaches can be adjusted. Since a beta-delayed neutron emission becomes strong if not dominating decaying channel for nuclei far stability, a proper neutron detector to study their properties is indispensable. To conduct the appropriate investigations, in the frame of the present thesis, in close collaboration with JINR (Dubna) a new detection system was constructed. It consists of 80 ³He-filled counters, 4π beta detector and a HPGe in order to measure simultaneously beta, gamma, neutron activity. The development of such a detection system system, currently installed at ALTO ISOL facility, was the first objective of the thesis. Then, during two experimental campaigns conducted to investigate beta decay properties of neutron rich nuclei in the neighborhood of N=50, N=82 the workability of the newly produced detection system was proven. In the vicinity of ⁷⁸Ni: half- lives and probability of beta-delayed neutron emission for ⁸º,⁸²,⁸³,⁸⁴Ga were measured. We were the first to observe the structure of ⁸¹,⁸² Ge via beta neutron gated gamma spectra. Thanks to the neutron detection channel the absolute intensities of beta decay were proposed for the first time. In the vicinity of ¹³²Sn the half lives of ¹²³Ag, ¹²⁴Ag, ¹²⁵Ag and ¹²⁷In, ¹²⁸In was measured. For the first time the beta delayed neutron emission was observed for ¹²⁶Cd, its Pn value also measured. Based on the data obtained we come to the conclusion that to figure out the relative contribution of allowed and forbidden decays more theoretical efforts should be done crossing the N=50 shell. Whereas in the vicinity of N=82 shell more experimental challenge are required.

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Caballero, Folch Roger. "First measurement of beta-decay half-lives and neutron emission probabilities in several isotopes beyond N = 126." Doctoral thesis, Universitat Politècnica de Catalunya, 2015. http://hdl.handle.net/10803/299373.

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In this work beta-decay half-lives and neutron-emission probability values have been experimentally determined for first time in several nuclei beyond the neutron-shell closure at N=126. To this aim the accelerator complex at the GSI center for heavy ion research (Germany), in combination with the FRS fragment separator, were employed. The beta-decay detection system consisted of a charged particle detector named SIMBA, which served to detect both ion and beta-particles, surrounded by an array of He-3 based neutron counters named BELEN. The half-life values of eighteen isotopes of Au, Hg, Tl, Pb and Bi were determined, as well as the neutron-branching ratios (or upper limits) for seven nuclei. A comparison of the present results with previous half-life measurements in this mass-region shows a generally good agreement, thus reflecting the systematic validity of the decay data available in this region. Compared to theoretical models, our results show a reasonable agreement for half of the analyzed isotopes, and large discrepancies of up to a factor of 10 for the other half. The measured neutron-branching ratios represent the first set of experimental data available in this mass-region for several isotopes. Owing to the absence of previous experimental results, the values reported here can be only compared with theoretical predictions. In summary, a fair compatibility is found between FRDM+QRPA calculations, which however are underestimating by a factor of 5 the neutron-branching ratio of Tl-215, which is the most exotic nucleus measured in this work.
En aquest treball s'han determinat, experimentalment i per primera vegada, vides mitjanes i valors de probabilitat d'emissió de neutrons de diversos nuclis amb més de 126 neutrons. Per tal d'obtenir les dades es va realitzar un experiment a les instal·lacions del centre d’investigació d'ions pesats GSI a (Alemanya), combinat amb el separador de fragments FRS. El sistema de detecció d'ions i desintegracions beta va consistir d'un detector de partícules carregades anomenat SIMBA, que estava envoltat per una matriu de comptadors proporcionals d’'He-3 que conformen el detector de neutrons BELEN. En total s'han determinat valors de vida mitjana de divuit isòtops d'or, mercuri, tal·li, plom i bismut, així com també la probabilitat d'emissió de neutrons (o llindars superiors) de set d'ells. Comparant els resultats amb les mesures de vides mitjanes anteriors en aquesta regió de nuclis s'observa un bon acord, reflectint la validesa de la sistemàtica de les dades existents. D’'altra banda, fent la comparació amb els models teòrics, els resultats mostren un acord raonable per la meitat dels isòtops analitzats, i grans discrepàncies, de fins a un factor 10, per l'altra meitat. Pel que fa a les probabilitats d'emissió de neutrons mesurades, essent la primera mesura experimental a la regió per a diversos nuclis, no és possible comparar amb altres els valors obtinguts. La única comparació que es pot avaluar és amb les prediccions teòriques. En resum, els resultats són compatibles amb el model FRDM + QRPA, no obstant s'observen discrepàncies considerables en alguns isòtops de fins a un factor 5, com és el cas del valor obtingut per Tl-215, que correspon al nucli més exòtic del qual s'’ha determinat la probabilitat d’'emissió de neutrons.

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47

Liland, Lukas. "Neutrino Emission From Supernovae : At what distance will it kill you?" Thesis, Uppsala universitet, Högenergifysik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-414990.

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48

Giraud, Quentin. "Corrections général-relativistes à l’émission radio et haute énergie des pulsars." Thesis, Strasbourg, 2020. http://www.theses.fr/2020STRAE024.

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Les étoiles à neutrons sont des astres extrêmement denses, plus denses qu’un noyau atomique, formés au cours d’une supernova. Un étoile à neutrons typique concentre ainsi une masse supérieure à celle du Soleil dans son diamètre d’une vingtaine de kilomètres. D’après la théorie de la relativité générale, qui décrit la gravité comme une déformation de l’espace-temps, le champ gravitationnel de ces étoiles devrait affecter de manière non négligeable les rayonnements électromagnétiques à proximité de celles-ci. Au cours de ma thèse, j’ai simulé les émissions radio et haute énergie provenant de l’accélération de particules le long des lignes de champ magnétique d’une étoile à neutrons dans la métrique de Schwarzschild pour savoir comment le rayonnement ainsi produit allait être affecté par les déformations de l’espace-temps au voisinage de l’étoile à neutrons
Neutron stars are very dense objects, denser than an atomic nucleus, formed during a supernova. A typical neutron star concentrates a mass superior to the one of the Sun in its diameter of around twenty kilometers. According to general relativity, which describes gravity as a space-time distorsion, the gravitational field of those stars should have a non-negligible impact on electromagnetic radiations close to them. During my thesis, I have simulated radio and high-energy emission originating from particules accelerated along the magnetic field lines of the neutron star inside the Schwarzschild metric to have an insight of how this kind of radiations would be affected by space-time distorsions in the vicinity of the neutron star

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Wickman, Erik. "Simulation of neutron generator assisted gamma emission tomography for inspection of fissile content in spent nuclear fuel." Thesis, Uppsala universitet, Tillämpad kärnfysik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-335161.

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This is a feasibility study of a new measurement technique for spent nuclear fuel. The technique combines gamma emission tomography with neutron activation analysis. The idea is to measure high-energy characteristic gamma from short-lived fission products and thereby verify the fissile material content in spent nuclear fuel assemblies. Simulations using MCNP were done to estimate the expected detector count rate for these characteristic gammas. The predicted count rate was too slow for the proposed technique to be of practical use. However, several improvements that could increase the count rate of the technique are suggested for further investigation of the prospects of this new technique.

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50

Saion, Elias bin. "On microdosimetry of neutrons of selectable energy in mixed (n,y) fields." Thesis, University of St Andrews, 1989. http://hdl.handle.net/10023/2640.

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Biological damage of tissue due to intermediate energy neutrons is generally known to be very important in radiobiology and radiation protection. However, there is no suitable method to determine the quality of these neutrons in particular in the working environment of mixed (n,y) radiation fields. In this thesis, an attempt is made to develop a dosimeter based on microdosimetric principles which has the capability for such a purpose. With this object the basic concepts of microdosimetry are reviewed and discussed with emphasis on their application for radiation protection and in designing of the dosimeter. Microdosimetry based on low pressure tissue-equivalent proportional counters (TEPCs) is a powerful technique for determining microscopic distributions of energy deposition and quality of ionizing radiations. However the energy deposition spectra of intermediate energy neutrons in mixed fields of fast neutrons can only be measured using TEPC in co-axial double cylindrical form by an appropriate choice for the thickness of the common tissue-equivalent (TE) dividing wall separating the inner and outer counters and by appropriate use of coincidence/anti-coincidence pulse arrangements. An analytical calculation for the response of the inner counter operating in coincidence/anti-coincidence modes with the outer counter was developed. However there will be some events, due to fast neutrons, which will contribute to the signals from intermediate energy neutrons and which cannot be removed by anti-coincidence. For these analytical corrections must be made. Also, the events associated with the dividing wall inherent in the system can contribute to the response of the inner counter and must be corrected by calculation. The calculation was possible due to the fact that recoil particles from intermediate energy neutron interactions have effective stopping powers and projected ranges which differ significantly from the continuous slowing down approximation (CSDA) values. By incorporating these the basic CSDA formulae for energy deposition spectra of neutrons could be extended down to intermediate energy neutrons of about 1 keV. A prototype co-axial double cylindrical TEPC capable of separating the component of neutrons (≤ 850 keV) in mixed (n,y) radiation fields was manufactured and tested. The thin wall dividing the inner and outer counters was fabricated from the standard A-150 TE plastic with the thickness equivalent to the range of 850 keV protons. The operational characteristics of the dosimeter were studied to determine its applicability for use in microdosimetry. The gas gain of the inner and outer TEPCs was measured at various simulated mean chord lengths and applied voltages. The results can be expressed according to Campion's equation within a given range of the electric field strength. The resolution of the inner TEPC measured at the operating voltages is in agreement with the theoretical prediction. A series of microdosimetric experiments were performed with mixed fields of 60Co gamma-rays and neutrons from the UTR-300 nuclear reactor and from 252Cf and 241Am-Be radioactive sources. Discrimination against fast neutrons of energy > 850 keV was achieved using an anti-coincidence unit specially designed for better efficiency of data acquisition. Discrimination against fast electrons due to photon interactions was also achieved. Spectra with anti-coincidence are dominated by slow protons and electrons. Their mean lineal energies are higher than those of spectra without anti-coincidence. The quality factor and dose equivalent for spectra with anti-coincidence are higher than the spectra without anticoincidence indicating the importance of intermediate energy neutrons in mixed fields. The quality factor and the corresponding dose equivalent corrected for saturation of lineal energy corresponding to 2 nm of ionization spacing is consistently higher than those derived from the absorbed dose based formulae, the biophysical implications of which are discussed. Suggestion for future developments for microdosimetry of intermediate energy neutrons in mixed fields are made and discussed.

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Dissertations / Theses on the topic 'Neutron emissions'

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